1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Conservation of energy with a mass and pulley system.

  1. Oct 25, 2011 #1
    1. The problem statement, all variables and given/known data
    Two boxes are attached to opposite ends of a rope passing over a frictionless pulley as shown below. The mass of Box A is 15kg and the mass of box B is 12kg. The system is originally at rest with the bottom of box A at a height of o.85m above the floor. When the system is released, the boxes will move. Use conservation of energy to determine the speed with which Box A will contact the floor.

    2. Relevant equations

    Ek= 1/2 mv^2/2

    3. The attempt at a solution
    I started off by drawing free body diagrams of each mass, one at rest, and one in motion.

    For mass A:
    at rest,
    Ft= Eg
    = mgΔh

    in motion,
    ƩFy= may
    Fg(A)-Ft= m(A)ay

    For mass B:
    at rest,

    in motion,
    Ft-Fg(B)= m(B)ay

    I'm not sure if my original statement of Ft=Eg is accurate... and from this point on I don't know where to go.
  2. jcsd
  3. Oct 25, 2011 #2
    Why not find the initial and final energies and equate them?
  4. Oct 25, 2011 #3
    As in, Etotal= Eg, Etotal'=Ek ?
  5. Oct 26, 2011 #4
    System is originally at rest. Hence initial energy = ...
    Final energy = ...
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Conservation of energy with a mass and pulley system.